The pre-collapse inward bowing of WTC2

[jaydeehess]

The issue is whether the deformation is from tension.... being pulled by trusses at 80" OC or whether it's from buckling.

Try this... the double trusses were connect to ever other facade column at mid spandrel ht. We are led to believe that the forces applied to ever other steel facade column... connected by a spandrel plate deformed the column without the truss connections the same amount as the columns with the truss connections. That is... the flat plate spandrels were so stiff (they were not) that they did not deform and were able to transfer the tensile forces to the the columns on either side.

If you believe that... I have a bridge I'd like to sell you at a great price.

Conclusion... inward bowing is basically the result of buckling from axial forces exceeding capacity. And yeah deformation increased over time.

Ok and the preference to bow inwards for all these columns on both towers is due to......

I am not disagreeing, just want an opinion.

 

[Mick West]

There is a wealth of information available. I'm not sure where it all is - or if it all is - on Metabunk. I'm a newbie here. And no matter which forum the info tends to be scattered rather than collated and packaged into single post explanations. I've done a bit of packaging over the years - not always easy to recover for several reasons.

However - Could you provide a list of some of the "many common conspiracies on 9/11" that interest you.

For your purpose I suggest it would be better if they were single or simple building block aspects rather than gross high level claims.

eg easier and more useful to you to address specifics such as "explosions were heard at WTCx" rather than a global claim such as "WTC Collapses were obviously CDed."

But not in this thread. This is the inward bowing thread.

 

[Seymour]

May I ask (after reading through)?

In regards to inward bowing....this discussion has been about WTC2, hit second (17 minutes after the impact on WTC1), yet as we know, WTC2 collapsed first. A salient fact is that the impact (from United 175) on WTC2 was well off-center. (**) (As compared to the American 11 impact on the other Tower). (** ETA: Also, United 175 had a different bank angle, on impact....American 11 was more level. Thus, United 175's wings would have been able to cause more of an impact "swath", vertically).

Does this add an element to the stresses that were involved in the collapse initiation?

IIRC, NIST said that 2 was closer to collapse at impact due to the off center hit. Therefore, it took less fire damage to initiate collapse initiation. This is why it collapsed first, not cuz it was hit lower and therefore had more weight above it. Which makes sense cuz if it had more weight above it, the columns would of been bigger/stronger.

 

[Seymour]

Ok and the preference to bow inwards for all these columns on both towers is due to......

I am not disagreeing, just want an opinion.

The NIST report details that as the trusses heated, but before they sagged, they expanded and would of pushed the ext columns outward. As they continue to heat, they begin to sag and pull them inwards.

It's important to remember though, that other things are going on while this is happening.In the beginning phase of the fires and truss heating, the core and ext columns haven't heated up much either, so the ext columns wouldn't of been seeing increasing loads from the heat creep induced shortening core columns. Plus, the ext columns wouldn't of been hot yet either, so they should of been able to be slightly out of alignment and not buckle outwards and rip the bolts from the truss connections.

Later, as the trusses heat up and sag, the core and ext columns would of been hotter. The loads would of been higher on the ext columns due to core column shortening. the ext columns would of been weaker due to being hotter.

A tug by the trusses. Increasing axial loads on weakening ext columns. So they bow inwards.

 

[Jeffrey Orling]

The NIST report details that as the trusses heated, but before they sagged, they expanded and would of pushed the ext columns outward. As they continue to heat, they begin to sag and pull them inwards.

It's important to remember though, that other things are going on while this is happening.In the beginning phase of the fires and truss heating, the core and ext columns haven't heated up much either, so the ext columns wouldn't of been seeing increasing loads from the heat creep induced shortening core columns. Plus, the ext columns wouldn't of been hot yet either, so they should of been able to be slightly out of alignment and not buckle outwards and rip the bolts from the truss connections.

Later, as the trusses heat up and sag, the core and ext columns would of been hotter. The loads would of been higher on the ext columns due to core column shortening. the ext columns would of been weaker due to being hotter.

A tug by the trusses. Increasing axial loads on weakening ext columns. So they bow inwards.

I don't buy that the truss could push the facade outward... the trusses were composite with the concrete and I doubt that the floor was expanding... but maybe... but the same rate???

 

[Seymour]

I don't buy that the truss could push the facade outward... the trusses were composite with the concrete and I doubt that the floor was expanding... but maybe... but the same rate???

Thermal expansion exists. It's not debatable.

I think Enik's fea showed the exact same thing.

Slight push out, followed by pull in as they sag.

 

[Jeffrey Orling]

Of course heat expands steel. I don't see the facade bulge did you?

 

[Seymour]

Of course heat expands steel. I don't see the facade bulge did you?

It wasn't much.

IIRC, just an inch or 2. Probably not observable.

But it's in the NIST report. You can check for yourself.

And of course there's Enik's (you know who I'm talking about, right?) thread at the 9/11 free forum. He says that there would of been some thermal expansion first, then pull in.

I'd call that independent confirmation of NIST's methods...

 

[Jeffrey Orling]

It wasn't much.

IIRC, just an inch or 2. Probably not observable.

But it's in the NIST report. You can check for yourself.

And of course there's Enik's (you know who I'm talking about, right?) thread at the 9/11 free forum. He says that there would of been some thermal expansion first, then pull in.

I'd call that independent confirmation of NIST's methods...

Yes and no . It seems to me the trusses would buckle before they pushed that robust facade at all. Did they push the core inward too? The IB is more likely buckling from stresses exceeding capacity... with the floors pulling inward. I don't think Enik modeled that one.

 

[Seymour]

It seems to me the trusses would buckle before they pushed that robust facade at all.

Seems? Ok then, don't be inquisitive and don't find out NIST's reasoning for it nor what they say about their fea. Your choice.

Did they push the core inward too?

Go find out.

The IB is more likely buckling from stresses exceeding capacity... with the floors pulling inward.

I agree with this. Maybe you misunderstood what I've said? The trusses weren't the only thing causing IB. IMO, the sagging trusses wouldn't have done much more than provide a nudge to make the bowing directional.

 

[Oystein]

It wasn't much.

IIRC, just an inch or 2. Probably not observable.

But it's in the NIST report. You can check for yourself.

And of course there's Enik's (you know who I'm talking about, right?) thread at the 9/11 free forum. He says that there would of been some thermal expansion first, then pull in.

I'd call that independent confirmation of NIST's methods...

I browsed (one of) Enik's threads on the former JREF forum the other day and had a look again at the 2002 paper by Scotsman - Usami? Not sure I have the name right. Anyway, his calculations, in the framework of a 2D-model (vertical cut, single pair of trusses for each floor, multiple floors) have the trusses pushing the EC out by 15 mm. I asked in that thread, early summer 2013 I think, if that would have been observable.

Also, among the "several things going on at the same time" he talks about is the differential heating of subsequent floors - a floor that's hotter than it's neighbors above and below would be pushing out more, and may subject these neighboring trusses to (increased) tension, which would in turn restrict how far the hot truss could push out, and subject it to more compression.

 

[econ41]

Enik is very good at using FEA but be cautious. He can fall for the false context/false starting assumptions traps.

(remember those are the errors that affect most of T Szamboti's work - specifically "Missing Jolt' and more recently with his "Girder Walk-off" claim for WTC7 where it was one of his many fatal or "not proven" errors - 5 from memory.)

Enik is self assured in his confidence with FEA - usually with good reason and I admire his efforts. However in one JREF thread he issued a challenge on precisely this OP point - viz could joist sagging have caused the Inwards Bowing. Newtons Bit responded and they had a bit of head to head discussion. Until I told them they were both wrong. NB ignored me and Enik counter attacked.

The issue of direct relevance to this thread - current discussion - is that floor joist sag could not cause the full extent of IB - that factor already recognised by Seymour Butz - possibly other members here.

Joist pulling would initiate bending THEN past a critical point (p delta is the technical reference) the now eccentric loading would self propagate IB under the existing axial load. So IB caused by two main factors - initiated by joist pull in then self propagates due eccentricity. Enik and Newtons got that bit right - the cynic in me suggests because they could hardly miss it using FEA which covers their arses on that aspect - asks them to make an explicit decision IIRC.

The point both went off the rails with on JREF - not under discussion here so far AFAICS - is that they applied the FEA to one joist - one column. 'Taint anywhere near that simple due to load sharing/load redistribution in the real event WTC collapses AND the simplifying assumption is invalid. That was the point I called them on. Enik and I settled our differences on 911 forum - he wasn't going to back down on JREF. NB maintains his stubborn attitude as always when he is wrong.

The other point here should not be in dispute - initial floor joist heating would cause an outwards push - whether or not it caused detectable outwards movement of the column. Not any significance in that except IIRC there was one academic paper claim that the outwards push falsified joist pull in. Nonsense.

So a broader caution. Take care when considering FEA work by current generation engineers. It does so much of the thinking for them that it is very easy for them to lose the plot.

Its an alligators v swamp draining situation for those who know the metaphor. More details if anyone wants them.

 

[econ41]

I browsed (one of) Enik's threads on the former JREF forum the other day and had a look again at the 2002 paper by Scotsman - Usami? Not sure I have the name right. Anyway, his calculations, in the framework of a 2D-model (vertical cut, single pair of trusses for each floor, multiple floors) have the trusses pushing the EC out by 15 mm. I asked in that thread, early summer 2013 I think, if that would have been observable.

I vaguely recall that thread - If you have a link Oystein I'll review the thread topic and post any relevant comments here.

 

[econ41]

.... The trusses weren't the only thing causing IB. IMO, the sagging trusses wouldn't have done much more than provide a nudge to make the bowing directional.

Exactly. Despite the megabytes of forum discussion chasing the false assumption that joist pull in was the only cause.

...and then the specialists going further and missing that all those columns were strongly tied together so much that calculations based on one joist pulling one column are.....will "dubious" do?

The single cause IB claims are one of what should be an infamous list of "both sides got it wrong" fiascos. Other candidates are - looking for the T Sz missing jolt when no such jolt was possible. AND arguments about whether or not ends of falling columns would make axial contact. Same error - it is the generic version of the false starting point error of "Missing Jolt".

 

[econ41]

Yes and no . It seems to me the trusses would buckle before they pushed that robust facade at all. Did they push the core inward too? The IB is more likely buckling from stresses exceeding capacity... with the floors pulling inward. I don't think Enik modeled that one.

It is a "how much" scenario Jeffrey. And the answer is "not enough to be detectable". The expanding joists would push the perimeter outwards. There is no threshold I am aware of below which a force has ZERO effect. BUT it would be so small as to be undetectable.

Totally different scenario but on one occasion there was a precision level measuring gadget installed inside the large concrete dam I managed.

200 feet of concrete below the gadget. And I walked to about 6-7 feet from the level and it went off scale - tilting towards the concrete floor where my weight was compressing the concrete. Now there was no way that even femr2 at his best could have measured that deflection by processing video taken from 1/2 mile away.

(Before anyone asks - it was measuring plate tilting activity or earthquakes in Timbuktu - something large scale geology.)

Back to our regular program.

 

[Seymour]

The issue of direct relevance to this thread - current discussion - is that floor joist sag could not cause the full extent of IB - that factor already recognised by Seymour Butz - possibly other members here.

I find it equally nutty when someone proposes that a core column drop of - what is the number, 9 feet? - was the most likely cause for IB.

Some people just have a genetic predisposition to go with the most complicated solutions.....

 

[econ41]

I find it equally nutty when someone proposes that a core column drop of - what is the number, 9 feet? - was the most likely cause for IB.

Agreed. A few months back T Sz made such a claim - core dropping caused the floor joists to pull in the perimeter with inward bowing.

Given the sequence of IB<>collpase I commended him for discovering "Delayed Action Gravity".

He was not amused.

Some people just have a genetic predisposition to go with the most complicated solutions.....

Or are acting out of desperation.

If you want to make your reputation by posting fantasies on the interwebs surely you would aim for at least some consistency/credibility.

I find it is much easier to post things that make sense. Takes a lot less effort.

 

[Oystein]

I vaguely recall that thread - If you have a link Oystein I'll review the thread topic and post any relevant comments here.

It's not a biggie. I brought it uop just to provide someone's take on how much the perimeter might get pushed out by expanding trusses - Usmani (that's the spelling now!) say "15 mm". I guess that's a good start for an order of magnitude estimate, even if his model is limited.

Anyway, it was in thist thread: Challenge: Demonstrate Sagging floor Trusses Pulling in Perimeter Columns
Usmani was introduced in post 6, your first comment on Usmani comes in post 24, I chime in at post 29 and mention the 15 mm in post 32.

Usmani's paper itself can be found here:
http://www.era.lib.ed.ac.uk/bitstream/1842/1216/1/WTCpaper.pdf
Column displacement over model time is shown in Fig. 12

 

[econ41]

It's not a biggie.

Understood - and I won't make it a biggie. Thanks for the links however.

Anyway, it was in this thread: Challenge: Demonstrate Sagging floor Trusses Pulling in Perimeter Columns Usmani was introduced in post 6, your first comment on Usmani comes in post 24, I chime in at post 29 and mention the 15 mm in post 32.

There is quite a serious discussion in that thread but not much of it we need to bring here at this stage. Better IMO if anyone is interested in discussing the engineering physics if we take it from scratch here rather than import reams of other peoples thoughts. Including mine.

However this was my overall impression of the Usami paper at that time - March 2013

I am still uncomfortable that the Usmani et al paper is yet another academic abstraction which seems to totally ignore observations of reality.

You know where I will come from in such a setting. Reality wins over academic abstraction. Esp if reality negates academic. Sorry Bazant et al.

However thanks for the comments - you did manage to get their paper back towards "floor pull in" as a real possibility. I will need to give it more thought.

I also note your comments about three dimensions - it is years since I tried to explain possible cascade failure propagation . but it has to be explained in 3D - you don't get load shedding from column/joist to adjacent/nearby column/joist in a 1D simplification. And load shedding is the key factor in a cascade. So what price academic 1d abstractions dealing with an event which is essentially 3D? You can explain an individual mechanism. But you cannot also address propagation. Cascade in this case being multiple mechanisms (at least two) plus propagation of failure and load shedding. I won't even attempt to comment further at this stage.

(Note I may have been drinking when i wrote that - my original has "2D" where it now has "1D" - dunno what I was thinking of.) (And nobody called me on the fumble. So much for serious discussions.)

I'll stand by the two key points - what really happened always trumps academic abstractions AND you cannot explain 3D cascade failures with 1D approximations.

 

[econ41]

...(Note I may have been drinking when i wrote that - my original has "2D" where it now has "1D" - dunno what I was thinking of.) (And nobody called me on the fumble. So much for serious discussions.)

I'll stand by the two key points - what really happened always trumps academic abstractions AND you cannot explain 3D cascade failures with 1D approximations.

Curiosity got to me and I had a more detailed look at the Usmani et al paper.

He used a 2D simplification - so that is where I got the 2D from. He was examining a 2D "narrow slice" - one joist and one perimeter column. And he seemed to fall for the same trap that later caught enik and Newtons Bit. (It definitely caught those two - I'm only 95% certain about Usmani - his paper is lengthy and somewhat dense and I'm not sufficiently motivated to read it through carefully in order to be 100% certain on that minor point.) The 2D approximation is not valid for the WTC scenario - useful to illustrate a principle - dangerous if used to support quantified outputs. The load shedding/load redistribution in the THIRD dimension cannot be disregarded.

Doesn't change my two point conclusion - tho' it would be more bullet proof if I had said this:

I'll stand by the two key points - what really happened always trumps academic abstractions which produce results which disagree with the real event AND you cannot explain 3D cascade failures with 1D approximations. Nor with 2D approximations in the context of WTC Twin Towers initiation.

And I'll leave it there - pedantic nit picking of my own comments.

 

[Oystein]

Curiosity got to me and I had a more detailed look at the Usmani et al paper.

He used a 2D simplification - so that is where I got the 2D from. He was examining a 2D "narrow slice" - one joist and one perimeter column. And he seemed to fall for the same trap that later caught enik and Newtons Bit. (It definitely caught those two - I'm only 95% certain about Usmani - his paper is lengthy and somewhat dense and I'm not sufficiently motivated to read it through carefully in order to be 100% certain on that minor point.) The 2D approximation is not valid for the WTC scenario - useful to illustrate a principle - dangerous if used to support quantified outputs. The load shedding/load redistribution in the THIRD dimension cannot be disregarded.
...

Final paragraph of Usmani's conclusion:

To achieve a firmer conclusion a 3D analysis would be necessary, also with a large range of reasonably realistic fire scenarios as carried out for this analysis. The current analysis clearly assumes that there is no support forthcoming from the directional orthogonal to the plane of the analysis. It is very likely, particularly for low temperatures that this additional support will delay failure and the the failing column will unload and the load will redistribute. This however could
not carry on ad-infinitum and collapse would eventually occur. Furthermore dynamic effects have not been considered in this analysis, which could either add to the destabilising forces or delay them or both. A3D dynamic analysis of this problem is the next logical step to take this investigation further.

Content from External Source

Looks to me as if Usmani does NOT "fall for the same trap" but is aware of it and knows the limits of applicability.

Anyway, this is drifting off-topic. As a reminder: I brought Usmani up since someone upthread had asked by how much the joists might push out the exterior columns and whether that would be observable, and Usmani provides an answer to the first question: About 15 mm.

 

[Seymour]

I find it equally nutty when someone proposes that a core column drop of - what is the number, 9 feet? - was the most likely cause for IB.

Oh I see it was 23 feet.. Even crazier.

And of course it brings up the subject whether or not the connections were strong enough to pull in the ext columns to any extent in the first place..

Usmani was an interesting read. Push out, then pull in made easier cuz it was over several stories.

 

[jaydeehess]

Meh! One thing is certain though, a slow inward bowing is not indicative of either thermitic or explosive cutting of anything.

 

[WeedWhacker]

One thing is certain though, a slow inward bowing is not indicative of either thermitic or explosive cutting of anything.

Man!!! Perfectly stated!!!!

 

[Playing Games]

Meh! One thing is certain though, a slow inward bowing is not indicative of either thermitic or explosive cutting of anything.

Don't get me wrong, I'm on your side, but why do these so called scientists claim thermitic or explosive was found in the dust and some believe collapse was due to controlled demolition? I distinctly remember on that day, watching it live on TV, both towers tilted with the south tower doing so more. Clearly when the north collapsed you can see how the top portion above point of impact buckled before the rest of it came down.

 

[jaydeehess]

Don't get me wrong, I'm on your side, but why do these so called scientists claim thermitic or explosive was found in the dust and some believe collapse was due to controlled demolition? I distinctly remember on that day, watching it live on TV, both towers tilted with the south tower doing so more. Clearly when the north collapsed you can see how the top portion above point of impact buckled before the rest of it came down.

Oh its a long and sordid tale of personal incredulity mixed with a skewed political world view.
Mayhaps I'll outline it a bit better on Saturday when I have time.

 

[econ41]

Man!!! Perfectly stated!!!!

And concise.

One of jaydeehess and my colleagues used to address the same principle but in a more subtle way. In the context of WTC7 and the Chandler free fall fiasco - but it is the same issue of sequence:

IIRC something like this "early motion is not consistent with an event > immediate collapse scenario" or words to that effect.

It was on a forum where blame the truther ranked higher than address what he is saying - and the "debunkers" ran to all corners of the planet to avoid facing that simple issue of truth.

Put in blunt laypersons language - IF you cut members of a structure using explosives or incendiary the building falls at that time. It doesn't wait.

Tony Szamboti repeated the same error about a year ago - on which occasion I parodied his claim because it required "Delayed Action Gravity."

 

[econ41]

Don't get me wrong, I'm on your side, but why do these so called scientists claim thermitic or explosive was found in the dust and some believe collapse was due to controlled demolition? ...

Put briefly it is a "faith based"position - not based on evidence and reasoning. I have suggested that it is a life style habit of "blame the Government" - 9/11 merely an excuse to call conspiracy. Many of those scientists are not from relevant disciplines of science. The few engineers who are pro-"truth" vocal show various combinations of "out of their depth" in the engineering AND strong commitment to their faith based obsession. At this stage I'll leave it for jaydeeheess to follow up on his "mayhaps".

Oh its a long and sordid tale of personal incredulity mixed with a skewed political world view.
Mayhaps I'll outline it a bit better on Saturday when I have time.

The floor is yours sir. Or rather "after you Sir!"

 

[jaydeehess]

Put briefly it is a "faith based"position - not based on evidence and reasoning. I have suggested that it is a life style habit of "blame the Government" - 9/11 merely an excuse to call conspiracy. Many of those scientists are not from relevant disciplines of science. The few engineers who are pro-"truth" vocal show various combinations of "out of their depth" in the engineering AND strong commitment to their faith based obsession. At this stage I'll leave it for jaydeeheess to follow up on his "mayhaps".

The floor is yours sir. Or rather "after you Sir!"

Oh dang, I forgot about this. Spent all afternoon on ISF instead. Next opportunity for me is Tuesday.

 

[Jeffrey Orling]

Enik is very good at using FEA but be cautious. He can fall for the false context/false starting assumptions traps.

(remember those are the errors that affect most of T Szamboti's work - specifically "Missing Jolt' and more recently with his "Girder Walk-off" claim for WTC7 where it was one of his many fatal or "not proven" errors - 5 from memory.)

Enik is self assured in his confidence with FEA - usually with good reason and I admire his efforts. However in one JREF thread he issued a challenge on precisely this OP point - viz could joist sagging have caused the Inwards Bowing. Newtons Bit responded and they had a bit of head to head discussion. Until I told them they were both wrong. NB ignored me and Enik counter attacked.

The issue of direct relevance to this thread - current discussion - is that floor joist sag could not cause the full extent of IB - that factor already recognised by Seymour Butz - possibly other members here.

Joist pulling would initiate bending THEN past a critical point (p delta is the technical reference) the now eccentric loading would self propagate IB under the existing axial load. So IB caused by two main factors - initiated by joist pull in then self propagates due eccentricity. Enik and Newtons got that bit right - the cynic in me suggests because they could hardly miss it using FEA which covers their arses on that aspect - asks them to make an explicit decision IIRC.

The point both went off the rails with on JREF - not under discussion here so far AFAICS - is that they applied the FEA to one joist - one column. 'Taint anywhere near that simple due to load sharing/load redistribution in the real event WTC collapses AND the simplifying assumption is invalid. That was the point I called them on. Enik and I settled our differences on 911 forum - he wasn't going to back down on JREF. NB maintains his stubborn attitude as always when he is wrong.

The other point here should not be in dispute - initial floor joist heating would cause an outwards push - whether or not it caused detectable outwards movement of the column. Not any significance in that except IIRC there was one academic paper claim that the outwards push falsified joist pull in. Nonsense.

So a broader caution. Take care when considering FEA work by current generation engineers. It does so much of the thinking for them that it is very easy for them to lose the plot.

Its an alligators v swamp draining situation for those who know the metaphor. More details if anyone wants them.

I think this is wrong. Truss would hold the facade from bulging out... and apply an asymmetric load causing them to buckle inward as the were sagging with a slight pull.. but not nearly (my guess) enough to budge those columns laterally without the axial buckling force.

 

[econ41]

Oh dang, I forgot about this. Spent all afternoon on ISF instead. Next opportunity for me is Tuesday.

No prob. Experience tells me your comments and mine would be very similar - and it was addressed to you. I'll wait.

EXCEPT
I would be tempted to re-state my "Twin Hypotheses"

 

[econ41]

I think this is wrong....

Do you Sander?. By my count I made 40 assertions of fact in that post. Did I get all of them wrong? Only a few? I still claim none of them wrong. Challenges on any of the specific assertions of fact welcomed. From any member.

...Truss would hold the façade from bulging out... and apply an asymmetric load causing them to buckle inward as the were sagging with a slight pull.. but not nearly (my guess) enough to budge those columns laterally without the axial buckling force.

That is essentially ONE of the points I am making - probably the central technical point. You are conflating some aspects which I was careful to separate and which occurred at different stages of sequence. Other than the confusion from that conflation the only difference between us is quantification of the relevant balance of contribution coming from joist pull in and axial buckling.

So the status I suggest is:
Several engineers have done FEA quantified work which says I'm right . And those engineers coming from truther and debunker sides. I've not done the analysis myself but I've run my engineering manager's eye over several of them. (Enik, Szamboti and Newtons Bit come to mind. Members of this forum may not be aware that my (then) 6yo grandson did experimental work to prove one of the supporting factors I have asserted.)

So bottom line seems to be that your gut feeling is different to my gut feeling. And I think I'll leave it there unless someone wants to explore further.

 

[Jeffrey Orling]

Ozzie,
I find your posts excellent and your reasoning sound. I am not entirely sure of your understanding of the pre release movements of the twins... Admittedly it's complex and hard to nail. I don't find the pull in by these flimsy trusses of the rather robust facade columns makes much sense. Bowing seems to be basically a buckling cause. Yes it is a gut feeling..

 

[econ41]

Ozzie,
I find your posts excellent and your reasoning sound. I am not entirely sure of your understanding of the pre release movements of the twins... Admittedly it's complex and hard to nail. I don't find the pull in by these flimsy trusses of the rather robust facade columns makes much sense. Bowing seems to be basically a buckling cause. Yes it is a gut feeling..

Understood and thank you. The combination of engineer <> architect has worked for you and I in many discussions across several forums.

Gut feelings are valuable and I know I can usually trust mine when it comes to engineering physics.

No point in me saying more at this stage except something caused the perimeter columns to buckle INWARDS rather than outwards. I'm happy that the small pull in from the floor joists could be enough to START the buckling heading inwards. And I'm 100% confident that all those lengthy discussions across forumland which have presumed that joist pull in was the only factor - ignoring p-delta - are WRONG. We agree on that and it has been the main point of my comments.

 

[jaydeehess]

Ok, you have somewhat heated columns and a slight inward force from sagging trusses. Introduce greater axial load due to load redistributions from impact damage and core column creep.
In strict Euler buckling there no preferential direction but with a small force inward you do have a preferred direction.

Does this non-engineer make himself clear?

 

[jaydeehess]

Don't get me wrong, I'm on your side, but why do these so called scientists claim thermitic or explosive was found in the dust and some believe collapse was due to controlled demolition? I distinctly remember on that day, watching it live on TV, both towers tilted with the south tower doing so more. Clearly when the north collapsed you can see how the top portion above point of impact buckled before the rest of it came down.

Oh dang, I forgot about this. Spent all afternoon on ISF instead. Next opportunity for me is Tuesday.

There is a segment of society that believes in an extra-governmental, organized shadow entity that causes events to occur to further their own self serving and secret agenda.
To this segment of society all events are suspect of having been caused by this shadowy group.
Thus they look for any small unknown, any slight flaw in official explanations of such events and specifically work towards bolstering their preconceived expectation of these events.

In this case it takes on a myriad, a wide spectrum of, claims. From extraterrestrials, through undefined space based power beams, faked or switched aircraft, to preplanted explosives or incendiaries.
One group points to a study of the dust that concluded thematic material was part of the dust matrix. Another study was done refuting that claim. Which to believe?

To my mind, the quantity of thematic material claimed in the dust samples would require that an enormous, quite ridiculous, quantity would have to have been initially loaded into the structures. Bear in mind that this is unreacted thematic material, leftovers that did not contribute to the collapse. It is further claimed that the long lasting, very hot rubble pile fires were effected by , again, leftover thematic material that did not contribute to the collapse. This the begs the questions, "how much was actually loaded in?; how was it done unobserved?; why was the burning of such enormous quantities unobserved?; why the huge overkill margin?", none of which are not addressed or at best woefully insufficient.

Furthermore the supposed thematic material has never been tested for a particularly thematic property, does it self oxidize, burn in a non-oxygenated atmosphere?

 

[econ41]

Ok, you have somewhat heated columns and a slight inward force from sagging trusses. Introduce greater axial load due to load redistributions from impact damage and core column creep.
In strict Euler buckling there no preferential direction but with a small force inward you do have a preferred direction.

Does this non-engineer make himself clear?

Yes to both questions. Your usual standard maintained.

My "engineer's gut feeling" also says:
a) Heating of perimeter columns may not have been very important cf the heating effect on joists which induced sagging;
b) The inward force from sagging was not a mere "nudge" - remember I didn't do the FEA but IIRC both sides of the argument agreed on a significant inwards pull - BUT not enough distance of pull for joist sag to cause all the bowing.

 

[Playing Games]

To my mind, the quantity of thematic material claimed in the dust samples would require that an enormous, quite ridiculous, quantity would have to have been initially loaded into the structures. Bear in mind that this is unreacted thematic material, leftovers that did not contribute to the collapse. It is further claimed that the long lasting, very hot rubble pile fires were effected by , again, leftover thematic material that did not contribute to the collapse. This the begs the questions, "how much was actually loaded in?; how was it done unobserved?; why was the burning of such enormous quantities unobserved?; why the huge overkill margin?", none of which are not addressed or at best woefully insufficient.

Furthermore the supposed thematic material has never been tested for a particularly thematic property, does it self oxidize, burn in a non-oxygenated atmosphere?

Are you saying that there was or claimed (unreacted) thermatic material found in the dust samples? How would and when was it loaded into the structures? Initially to me it means it was put in place during construction. If it was placed during the 911 planning phase I can't see how it would be possible (occupied by many tenants and official WTC employees) for someone not to notice.

 

[econ41]

Are you saying that there was or claimed (unreacted) thermatic material found in the dust samples? How would and when was it loaded into the structures? Initially to me it means it was put in place during construction. If it was placed during the 911 planning phase I can't see how it would be possible (occupied by many tenants and official WTC employees) for someone not to notice.

All good stuff - and there are several "bigger picture" issues about thermXte. Essentially it was an ego serving ploy by S Jones which has become a "red herring" BUT we are heading too far "off topic". If anyone want to discuss thermXte - take it to another thread and I may put in my 2c worth.

For the "on topic" record I don't think thermXte was involved in heating the floor joists.

 

[jaydeehess]

Yes to both questions. Your usual standard maintained.

My "engineer's gut feeling" also says:
a) Heating of perimeter columns may not have been very important cf the heating effect on joists which induced sagging;
b) The inward force from sagging was not a mere "nudge" - remember I didn't do the FEA but IIRC both sides of the argument agreed on a significant inwards pull - BUT not enough distance of pull for joist sag to cause all the bowing.

Not saying that heating of (mostly the inward side of) the perimeter columns was a major contributor, just that even 250C heating would contribute yet another slight allowance for bowing. Perhaps by linear expansion on the inward side more than by loss of strength.
If I were to guess what the greatest contribution was I would say load redistribution. Sagging trusses simply offered a mechansim by which bowing was preferentially inward over several floors where sagging trusses were.